Ball and socket assembly

ABSTRACT

A ball and socket assembly including a ball component with a notch formed therein. The socket is a one-piece structure including an opening sized to receive the ball component.

FIELD OF THE EMBODIMENTS

Various embodiments disclosed herein are directed to ball in socketassembly designs.

BACKGROUND

Many ball and socket designs have been developed in order to facilitaterelative angular movement between two components. Typically, the balland socket designs include a spherical knob that is fitted into a socketdefining an interior which receives the ball. One variation of the balland socket design includes a socket having an opening that is slightlysmaller than the radius of curvature for the ball member. When the ballmember is coupled with the socket, the ball member is permanentlysecured within the socket. Alternatively, the entry within the socket isadjustable to allow the ball member to be easily inserted into orremoved from the socket.

In another variation, the external profile of the ball member isadjustable (i.e., expandable) to secure the ball member within thesocket. In yet another variation, the ball member includes one or moregrooves or surfaces that correspond to ridges provided on the openingrim of the socket. The ball member may be coupled to the socket if thegrooves are aligned with the corresponding ridges of the socket. Onceinserted, the ball member is rotated to secure the ball member withinthe socket.

While current designs are useful, there is a continuing need for balland socket designs having a significant range of motion and a maximumhigh tolerance load surface area. Moreover, there is a need for a socketembodying significant structural integrity and reduced wear under highpeak stresses while assuming a low profile.

The present disclosure address these and other needs.

SUMMARY

Briefly, and in general terms, the present disclosure is directed to aball and socket assembly. In various aspects, the disclosed assembliesembody structure facilitating significant ranges of motion of a ballcomponent with respect to the socket. In this regard, in contemplatedapproaches, deformation of the ball or socket can be avoided. Moreover,due to the particular shape of the ball component, a single piece socketis possible as is an assembly having a low profile. In particular, theball can assume a spheroid shape. The socket captures the ball withoutdeformation of the socket or ball to prevent the ball from being able tobe pulled out of the socket during use while also providing a contactsurface on the ball and socket with no separation line to minimize wearduring use. Such approaches have an application across fields of art andin particular, in medical applications. In one approach, the ballcomponent can include a notch formed by removing a volume of materialfrom its body.

In one particular aspect, a ball and socket assembly can include a jointcomposed of a hook-in ball and one-piece socket design. The hook-in balland one-piece socket are coupled together in a first orientation andoperates in various other different distinct orientations. In anoperational configuration, the hook-in ball and one-piece socket providea range of motion that is not overly restrictive, but rather provideranges of motion desired for a particular or wide ranges ofapplications. Depending upon the embodiment, the hook-in ball andone-piece socket joint is designed to allow a range of motion includinga 360 spin degrees, about a longitudinal axis of the component, ±17.5(35) degrees of movement along a minor axis of an opening to the socket,and ±77.5 (155) degrees of movement along a major axis of the socketopening. In one preferred approach, a 0.002 diametrical clearancebetween the ball component and the socket is contemplated.

The hook-in ball and one-piece socket is designed to provide a durablejoint that maintains functionality over a large number of cycles. Thedurability of the joint is attributable to cooperation of the hook-inball and one-piece socket. Where there are split lines on wearingsurfaces, relative motion between bearing surfaces can more quickly leadto structural failure. Additionally close tolerances between movingparts are more difficult to achieve and maintain. The hook-in balldesign eliminates the need to apply large forces to insert the ball intothe socket, thereby avoiding an approach relying on deformation of thesocket or ball component to accomplish a coupling of the members.Consequently, due to an ability to employ a substantially non-deformablesocket (or ball), stresses as well as wear of the ball and socket areminimized. Additionally, the complementary design of the hook-in balland one-piece socket provides a joint with a yield strength that isgreater than the maximum stresses applied at expected maximum loads,which improves longevity of the joint.

Generally, the hook-in ball defines a notched spherical head that iscoupled to a shaft. The notched portion of the spherical head is formedby removing a volume of material. The notched portion can have variousshapes, sizes, or locations on the spherical head. In a preferredapproach, the notch surface defines a saddle shape formed by six angledsurfaces. It is also contemplated that one or more notch portions can beprovided on the spherical head. The notch on the spherical head reducesthe effective cross-section of a portion of the head so that theresultant hook-in ball can fit into a one-piece socket having arestricted opening. That is, the hook-in ball is only insertable intothe one-piece socket when the notch on the spherical head is properlyoriented relative to the opening of the socket. Thus, when constrainedfor motion in orientations distinct from an insertion orientation, thesocket securely retains the ball component.

Another embodiment of the hook-in ball is formed of two parts, a notchedspherical head coupled to a shaft and a filler component. The fillercomponent is a volume of material that is inserted into the notch of thespherical head to form a complete sphere. In this embodiment, thenotched spherical head can be inserted into a one-piece socket. Thefiller component is then secured within the notch of the spherical headto form the completed sphere. The filler component can be removed fromthe spherical head to allow disassembly of the ball component from theone-piece socket.

According to one embodiment, the one-piece socket component is composedof a socket cavity having a restricted opening and includes curved wallshaving interior surfaces defining a bearing surface, wherein the bearingsurface further defines a contour forming a portion of a sphere. Theopening to the socket has a dimension along a major axis that isconfigured to receive the hook-in ball. The restricted opening canassume various shapes and sizes, such as elongated, symmetrical,asymmetrical, or other shapes. Depending upon the application, therestricted opening can be shaped to accommodate different ranges ofmotion. For example, the restricted opening can be shaped to allowlinear motion (e.g., motion in one plane), curvilinear motion(non-planar motion), and/or crossing motions (i.e., motions in planesthat intersect). Optionally, certain embodiments of the one-piece socketcan also include one or more cut-outs that are in communication with thesocket cavity.

In a preferred embodiment, the components forming the ball and socketassembly are formed from cobalt chromium. Various coatings are alsocontemplated. Thus, one or more of the ball and socket components can becoated with a ceramic material.

Other features and advantages will become apparent from the followingdetailed description, taken in conjunction with the accompanyingdrawings, which illustrate by way of example, the features of thevarious embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a side view of one embodiment of a ball.

FIG. 1B is a front view of the ball shown in FIG. 1A.

FIG. 2A is a side view of another embodiment of a ball.

FIG. 2B is a front view of the ball shown in FIG. 2A.

FIG. 2C is a side view of a further embodiment of a ball.

FIG. 2D is a side view of yet another embodiment of a ball.

FIG. 3A is a side view of another embodiment of a ball.

FIG. 3B is a front view of the ball shown in FIG. 3A.

FIG. 4A is an exploded side view of another embodiment of a componentball.

FIG. 4B is a side view of the component ball of FIG. 4A in an assembledstate.

FIG. 5A is a top view of one embodiment of a one-piece socket.

FIG. 5B is a top view of another embodiment of a one-piece socket.

FIG. 6 is a perspective view of one embodiment of a one-piece sockethaving a cut-out.

FIGS. 7A-D are top views of one-piece sockets having different ranges ofmotion.

FIGS. 8A-B illustrate the orientation of the ball relative to one-piecesocket when inserting the ball and after placement within the one-piecesocket.

FIG. 8C illustrates the orientation of the ball relative to theone-piece socket when the ball and one-piece socket are in anoperational configuration.

FIGS. 9A-C illustrate the coupling and operational orientations of theball shown in FIGS. 3A-B and the one-piece socket shown in FIG. 7.

FIG. 10 illustrates one embodiment of a ball and socket assembly as ajoint prosthesis for a finger joint.

FIGS. 11A-B illustrates one embodiment of a ball and socket assembly asa joint prosthesis for a hip joint.

FIG. 12 illustrates one embodiment of a ball and socket assembly as ajoint prosthesis for an elbow joint.

FIG. 13 illustrates one embodiment of a ball and socket assembly as ajoint prosthesis for an ankle joint.

FIG. 14 illustrates one embodiment of a ball and socket assembly used inan extra-articular mechanical energy absorbing system.

DETAILED DESCRIPTION

Various of the disclosed embodiments are directed to a ball and socketassembly. In the contemplated approaches, the assembly includes a ballwith a portion of a non-load bearing surface removed and a one-piecesocket. The components of the assembly cooperate to provide asignificant range of relative motion. Also, the assembly is configuredsuch that it assumes a desired low profile.

The ball and one-piece socket assembly can be used in any desirablemechanical application. In a medical specific application, the assemblycan be employed to completely or partially replace and/or complement thehip, finger, toe, knee, elbow, ankle or other joints. In addition, theball and socket assembly may be used in an extra-articular mechanicalenergy absorbing system.

In one embodiment, the ball can define a spheroid that includes a headwith a notch, cavity or undercut that is coupled to a shaft. The notchedor cavitied portion of the head is formed by removing a volume ofmaterial from the head. The notched or cavitied portion can have avariety of shapes, sizes, or locations on the ball component. It is alsocontemplated that one or more notch, cavity or undercut portions can beprovided on the head. The notch, cavity or undercut on the head reducesan effective cross-section of a portion of the head so that the ball canfit into a one-piece socket having a restricted opening withoutdeforming the ball or socket thus creating a ball and socket assemblythat can withstand substantial loads and peak stresses with minimalwear. That is, the ball is insertable into the one-piece socket when thenotch, cavity or undercut on the spherical head is properly orientedrelative to the opening of the one-piece socket.

Generally, the one-piece socket is composed of a socket cavity having arestricted opening. The restricted opening is smaller than an effectivecross-sectional dimension of the socket cavity. In certain embodiments,the opening is shaped to restrict the range of motion of the ballcomponent. The socket cavity has approximately the same diameter as thespherical head. The socket cavity is defined by curved walls that areshaped to receive an outer surface of the head of the ball component. Ina preferred approach, the curved walls of the socket cavity form aportion of a spherical shape.

In one embodiment, the ball and socket assembly includes a ball and aone-piece socket which are coupled together in a first orientation andoperates in various orientations distinct from the first orientation. Inthe first orientation, the notched portion of the ball is aligned withthe restricted opening of the one-piece socket such that insertion ispossible. The smaller effective cross-section of the notched portion ofthe head allows the head to be inserted through the opening of thesocket cavity. Once the ball head is inserted into the socket cavity, itis rotated about (i.e., rotated around the longitudinal axis of theshaft) to secure the ball within the socket cavity. In operation, theball is constrained so that the notched portion does not contact theinner surface of the socket cavity during the entire range of motion ofthe ball within the socket cavity. As a result, the ball cannot bedislocated from the one-piece socket. If a force is applied to the ballhead along the longitudinal axis of the shaft, this force is absorbed bya bearing surface area of the socket cavity.

The ball and socket assembly can be made from materials such astitanium, cobalt chrome (e.g., Biodur CCM Plus), ceramic, or otherdurable materials that produce a minimal amount of particulate materialor, if particulate material is generated, the smallest size ofparticulate material. Additionally, the surfaces of the ball and theone-piece socket are highly polished and can be coated with a ceramic orother material. In one embodiment, the socket cavity and the outersurface of the ball component each have a surface finish that ispolished to a mirror-like finish. Additionally, the selected materialsfor the ball and socket cavity to embody a yield strength that isgreater than the maximum stresses at maximum loading that may applied tothe components. Moreover, preferably the selected materials maintainfunctionality of the components for over two million loading cycles.

Referring now to the drawings, wherein like reference numerals denotelike or corresponding parts throughout the drawings and, moreparticularly to FIGS. 1A-9C, there are shown various embodiments of aball and socket assembly. More specifically, FIGS. 1A-4B illustratevarious embodiments of a hook-inball having a shaft, and FIGS. 5A-7Dshow various embodiments of a one-piece socket. FIGS. 8A-8C and 9A-9Cdepict the orientation of the ball component relative to the socketduring assembly. FIGS. 10-14 include exemplary applications of the balland socket assembly in joints within the body.

Turning now to FIGS. 1A-B, a hook-in ball component 10 is composed of aball component 12 coupled to an elongated shaft 14. The ball component12 includes a notch, cavity or undercut 16. The ball component and theelongated shaft 14 define a unitary structure. It is contemplated,however, that the ball component and the shaft may be distinct partsthat are coupled together. The notched portion 16 of the spherical head12 results from removing a volume of material from the head. As shown inFIGS. 1A-1B, the notched portion 16 can define a generally saddle shape.In one approach, the saddle shape can be formed by six planar surfaces.Such surfaces can also have a curvature to them. The notched portion 16on the ball head 12 reduces the effective cross-section of a portion ofthe head so that the head can pass through an opening formed in a socketcomponent. As those skilled in the art will appreciate, the notchedportion 16 may be any size, depth, location, or shape so long as theeffective cross-section of a portion of the spherical head 12 is reducedas compared to the widest cross-section of the head. A smallest possiblenotch may be employed to provide a ball and socket assembly with arelatively larger interfacing surface.

The elongated shaft 14 has a diameter less than the dimension at thewidest point of the spherical head 12 as shown in FIGS. 1A-1B. It iscontemplated that the shaft may have any length, shape, diameter(variable or constant) depending upon the intended application.

FIGS. 2A-2D illustrate other embodiments of a ball socket assembly. Asshown in FIGS. 2A-2B, a hook-in ball component 10 can have a notchedspherical head 12 and an elongated shaft 14. Here, the notched portion18 is defined by a concave surface formed in a side of the head of theball component. It is contemplated that the head 12 can include one ormore such notched portions 18 which can be located anywhere on thespherical head 12 for desired purposes. For example, see FIG. 2C whichdepicts a notched portion 16 of the spherical head 12 that is locatedapproximately along a longitudinal axis running through the component.Again, in other embodiments, the notched portion 16 (i.e., centered oroff-axis) is positionable anywhere on the surface of the head 12 so longas a portion of the head has a reduced diameter. In this regard,reference is made to FIG. 2D, where the ball component 12 includes anotch 16 having an opening directed generally parallel to shaft 14.

FIGS. 3A-3B illustrate yet another embodiment of a ball component 10having a notched head 12 and a shaft 14. As best shown in FIG. 3B, anotched portion 20, 22 extends to opposite sides of the head 12. Portion24 of the head 12 forms a surface for engaging a socket component.

As shown in FIG. 3A, the notched portion 20 includes two surfaces 26, 28that are angled with respect to one another. A first surface 26 of thenotched portion 20 can be formed generally perpendicular to alongitudinal axis of the shaft 14, and a second surface 28 can approachgenerally parallel relatively with a longitudinal axis extending throughthe component. In one embodiment, the notched portion 20, 22 isdimensioned approximately equal to the outer diameter of the shaft 14along a longitudinal dimension. Alternatively, the dimension of thenotched portion 20, 22 is greater than the outer diameter of the shaft14.

FIGS. 4A-4B illustrate another embodiment of a ball component 10. Theball component includes a notched head 12 fixed to or otherwise forms anintegral unit with a shaft 14. As depicted in FIG. 4A, the head 12 has acavity or notched portion 16 having a plurality of openings 34positioned on the surface of the notched portion. A filler component 30is further provided. The filler component 30 is a volume of materialthat is shaped and sized to mate with the notched portion 16 of the head12. The filler component 30 includes a plurality of prongs 34 thatextend away from a surface of the filler component. The prongs 34 aresized, shaped, and positioned on the filler component 30 to be pressfitted into the openings 34 on the notched portion 16. A completelyspherical head is formed when the filler component 30 is coupled to thenotch portion 16 as depicted in FIG. 4B. The filler component 30 isinserted into the notched spherical head 12 after the head is insertedinto a socket. In this way, the two piece ball component can be placedwithin a socket having a relatively small opening and a relatively largebearing surface. In one embodiment, the filler component 30 isreversibly inserted into the head 12 (i.e., the filler component isremovable). Alternatively, it is possible that the filler component 30may be permanently fixed to the notched spherical head 12.

Turning now to FIGS. 5A-7D, various embodiments of a socket componentare shown. More specifically, FIG. 5A depicts a one-piece socket 50having a socket cavity 52 and an opening 54 for accessing the socketcavity. The socket cavity 52 includes a contiguous surface that definesa spherical space. As shown in FIG. 5A, the socket cavity 52 has anopening having a major axis dimension D and a minor axis dimension D₁.Thus configured, the socket cavity is able to secure a hook-in ballcomponent 10 having a notched head 12 with an effective minimumcross-sectional dimension which can be received within the dimensions ofthe major and minor axis. The ball head 12 and the socket cavity 52 aresimilarly dimensional in order to prevent the translation (side to sidemovement) of the head within the socket cavity. For example, the socketcavity 52 can have tolerances of approximately 0.002″ diametricalclearance with the ball (nominal), approximately 0.0005″ on balldiameter, and approximately 0.0002″ on sphericity.

As stated, the opening 54 of the one-piece socket has a minor axisdimension D₁ that is smaller than the diameter D of the socket cavity.As a result, a completely spherical ball having a diameter D would notbe insertable into the socket cavity 52 without exerting a large forcethat would cause deformation of the opening 54 or to the surface of theball component. In order to avoid this situation, the ball componentincludes a notched portion (see FIGS. 1A-4A), which reduces theeffective cross-section of a portion of the ball, so that it can passthrough the opening and be secured within the socket cavity 52. Theopening 54 includes structures 56, 58 which define the shape of theopening. This structure 56,58 can be symmetrical or alternatively,asymmetrical in shape.

The opening 54 and walls defining the socket secure a ball component(not shown) within the socket cavity 52 without overly restricting therange of motion. For example, the socket geometry allows 360 degrees of“spin” rotation, up to or greater than 35 degrees of motion of the ballcomponent along the minor axis of the opening and up to or greater than77.5° of motion of the ball component along a major axis of the opening.As those skilled in the art will appreciate, the range of motion may berestricted or expanded based upon the intended application so thatdegrees of matter in X, Y or Z axes can be configured as necessary.

FIG. 6 depicts another embodiment of a one-piece socket 50. The socket50 includes a socket cavity 52 with a bearing surface having a dimensionD and an opening having a dimension D₁, wherein D>D₁. The shape of theopening 54 is defined by the wall structures 56, 58. As shown in FIG. 6,one portion of the structure 58 includes a cut-out 60 that extends intothe socket cavity 52. It is contemplated that the size, shape, andlocation of the cut-out 60 may be varied from FIG. 6.

With reference to FIGS. 7A-7D, a number of sockets 50 are shown havingvariously shaped openings 54 that define the directions of the range ofmotion. FIG. 7A depicts a socket 50 having an elongated opening 54 thatdefines a linear motion (i.e., motion in one plane). FIG. 7B shows aone-piece socket 50 having a curved opening 54 that defines acurvilinear motion. FIG. 7C illustrates a socket 50 having an X-shapedopening 54 that defines a crossing motion (i.e., linear motions inintersecting planes). FIG. 7D shows a one-piece socket 50 having anintersecting curved opening 54 that defines a curved crossing motion(i.e., non-linear motions in intersecting planes).

With reference to FIGS. 8A-8C, one exemplary method of inserting andlocking of a hook-in ball in a one-piece socket is shown. As shown, thenotched head 12 is oriented such that the portion of the head having thedimension D₂ is oriented over the opening (having a dimension D₁) of thesocket 50. The cross-sectional dimension D₂ of the head 12 needs to besmaller than the dimension D₁ of the restricted opening in order for thenotched head to be inserted through the restricted opening. As shown inFIG. 8A, the notched portion 18 straddles a perimeter structure 56 ofthe restricted opening, and the shaft 14 is rotated in direction R toinsert the head 12 into the socket cavity 52.

FIG. 8B shows the head 12 of the hook-in ball positioned within thesocket cavity 52 of the socket. The hook-in ball is rotated about thelongitudinal axis of the shaft 14 in order to secure the hook-in ballwithin the socket cavity 52. The notched head 12 only needs to beslightly rotated to be secured within the socket cavity. For example,but not by of limitation, the spherical head 12 can be rotated 5°-10° tosecure the head 12 within the cavity 52. In an engaged orientation, itis contemplated that pull forces of at least 260 lbs is required toseparate the head 12 from the socket cavity 52. Additionally, as shownin FIG. 8C, the notched portion 18 is oriented such that it faces awayfrom contact with the socket cavity 52 surface when a longitudinal loadalong the axis of the shaft 14 is applied to the spherical head. Stateddifferently, when a load is applied to the joint, the contact areabetween the spherical head 12 and the socket cavity 52 consists of the acurved portion of the head and the bearing surface of the socket cavity.

FIGS. 9A-9C illustrate another exemplary method of inserting and lockingof another embodiment of a hook-in ball 10 within socket 50. Alongitudinal axis of the hook-in ball 10 is first aligned generallyperpendicular to the socket cavity 50 as shown in FIG. 9A. As such, thehook-in ball 10 is oriented so that the notched portions 20, 22 areinserted into the cut-out portion 60. Also, a top of the head 24 isinserted into the opening 54. Once the top portion of the head has beeninserted through the opening 54, the hook-in ball 10 is rotatedapproximately 90° in direction R to the configuration shown in FIG. 9B.The hook-in ball 10 may be secured within the socket cavity by rotatingthe hook-in ball a few degrees or as much as 90°.

Referencing FIGS. 10-14, various applications of the hook-in ball andsocket assemblies 100 are depicted. As shown in FIG. 10, the assembly100 is used in a finger 102. A stem 62 of the socket 50 is inserted intoan end of bone (e.g., metacarpal bone). As shown in FIG. 10, the stem 62has a tapered diameter, but it is contemplated that the stem may have aconstant outer diameter. Optionally, the stem 62 may be etched,roughened, or coated with osteointegrating materials. The opening of thesocket 54 is generally shaped to allow the natural range of motion ofthe finger joint (i.e., flexion and extension in a plane). The geometryof the opening can be modified from a linear motion to a curvilinearmotion or cross trajectories for the thumb or other multi-axial jointswithin the body.

The hook-in ball 10 of the assembly 100 may be attached on an oppositeside of the joint such as by inserting a shaft 14 into the end of theother bone of the joint (e.g., proximal phalanges). Like the stem 62 ofthe socket 50, the shaft 14 of the hook-in ball may have a variable orconstant diameter or an osteointegration surface provided on the outersurface. Optionally, the shaft 14 includes a keel 104 that extends awayfrom the outer diameter of the shaft of the hook-in ball. Additionally,the keel 104 may be provided on the stem 62 of the socket 50. The keel104 stabilizes the hook-in ball 10 or the socket 50 by preventingrotation of these components.

The use of the hook-in ball and socket assembly 100 as a finger jointprosthesis decreases the rate of joint dislocation as the pull outforces required to remove the hook-in ball from the socket cavity arevery large. Additionally, the assembly 100 is made of materials such as,but not limited to, titanium, cobalt chrome, or stainless steel whichhave increased durability as compared to silicone or polymericprosthesis. Additionally, the assembly 100 has improved stability ascompared to other finger joint prosthesis.

The hook-in ball and socket assembly 100 may be used in any of thefinger joints (e.g., between carpals and metacarpals, between theproximal phalanges and middle phalanges, or the middle phalanges and thedistal phalanges). In another application, the assembly 100 may be usedto partially or completely replace toe joints.

FIGS. 11A-11B illustrate the use of the hook-in ball and socket assembly100 as a hip joint prosthesis. As shown in FIG. 11A, a hook-in ball 10is coupled to a body extension 106. The hook-in ball 10 and bodyextension 106 are coupled to the femur 106 as shown in FIG. 11B.Alternatively, only the hook-in ball 10 component is used to replace thehead of the femur 106. The socket 50 is used to replace the natural hipsocket in the pelvic bone 110. As described above, the hook-in ball 10and the socket 50 can include osteointegration surfaces, keels, or otherstabilizing structures. The use of the hook-in ball and socket assembly100 decreases the rate of joint dislocation as the pull out forcesrequired to remove the hook-in ball 10 from the socket 50 are verylarge. Additionally, the geometry of the socket opening can be shaped toprovide limited/controlled excursion of the hook-in ball within thesocket.

FIG. 12 illustrates the use of the hook-in ball 10 and socket 50assembly as an elbow joint prosthesis. Similar to the other jointprostheses previously disclosed, the use of the hook-in ball 10 and thesocket 50 can reduce the rate of dislocation of the joint. Additionally,as an elbow joint prosthesis, the hook-in ball and one-piece socketjoint 100 eliminates the need for the radius bone since the assembly 100can rotate as well as translate to approximate natural motion.

As shown in FIG. 13, the use of the hook-in ball 10 and socket 50assembly is contemplated as an ankle joint prosthesis. The ankle jointprosthesis shown in FIG. 13 has similar benefits to the joint prosthesesshown in FIGS. 10-12. Additionally, the hook-in ball 10 and socket 50can provide a better range of motion as compared to other ankleprostheses.

FIG. 14 illustrates the use of the hook-in ball 10 and the socket 50assembly as joints within an extra-articular mechanical energy absorbingor manipulating system 140. According to one embodiment, the implantablesystem 140 is composed of an absorber 142 that spans a joint (e.g., theknee as shown in FIG. 14) and off-loads forces at the joint. The ends ofthe absorber 142 are multi-dimensionally, pivotally coupled to basecomponents 144, 146 via the hook-in ball and socket assembly 100. Theassembly 100 allows the absorber 142 to track the natural movement ofjoint (e.g., knee joint).

The hook-in ball and assembly socket assembly 100 shown in FIGS. 10-14are low-profile connections that may be used in various parts of thebody anatomy. The assembly 100 is designed to provide maximum loadcontact area (between the ball component surface and the socket cavity)thereby improving wear performance of the joint. Additionally, theassembly 100 is self-lubricating when implanted within the body as thestructure is exposed to body fluids and in a lipid rich environment(i.e., in contact with or exposed to fatty tissue), thereby furtherimproving wear performance of the joint. Accordingly, it is contemplatedthat the components of the assembly do not need to be frequentlyreplaced.

As those skilled in the art will appreciate, the disclosed embodimentsof the hook-in ball and socket assemblies may be combined to form ajoint for various contemplated purposes. Additionally, the pivotconnections disclosed herein may be used in mechanical arts requiring aconnection that allows for relative angular movement between twocomponents.

The various embodiments described above are provided by way ofillustration only and should not be construed to limit the disclosedembodiments. Accordingly, certain elements and structures of oneapproach can be substituted for or added to complement other approaches.Those skilled in the art will readily recognize various modificationsand changes that may be made to the disclosed embodiments withoutdeparting from the true spirit and scope of the claimed invention, whichis set forth in the following claims.

What is claimed is:
 1. A ball and socket assembly of an implantablemedical device, comprising: a ball component including a ball and ashaft extending from the ball, the ball component formed from a unitarypiece of biocompatible material and including an undercut extending fromthe shaft about less than a full circumference of the ball component,the undercut having a longitudinal length parallel to the shaft that isless than an undercut circumferential width transverse to thelongitudinal length; and a socket component, the socket component beingformed from a single piece of biocompatible material wherein the ballcomponent is held in the socket assembly by the socket component.
 2. Theassembly of claim 1, wherein the ball component includes a volume ofmaterial removed from a portion of the ball component to allow the ballcomponent to be hooked into the socket component.
 3. The assembly ofclaim 1, wherein the socket includes an opening having a more narrowdimension along a minor axis and a less narrow dimension along a majoraxis.
 4. The assembly of claim 3, wherein the ball component is hookedinto the opening with the shaft on the ball component oriented generallyperpendicular to the major axis with a recess formed by the volume ofmaterial removed facing into the socket.
 5. The assembly of claim 1,wherein the unitary ball component includes an elongated shaft.
 6. Aball and socket assembly, comprising: a hook shaped ball componentincluding a ball and shaft configured as a single one-piece componentwith a bottom half of the ball surrounding the shaft and including anundercut on a bottom half of the ball component, the undercut extendingabout less than a full circumference of the ball component to form thehook shape; and a one-piece socket component including an opening;wherein the ball component is inserted in the opening of the socketcomponent in a non-operating orientation and is constrained to operatein various orientations distinct from the non-operating orientationwhereby the ball component and socket component will not dislocate fromeach other.
 7. The assembly of claim 6, wherein the opening is smallerthan a diameter of the ball component in at least one direction.
 8. Theassembly of claim 6, wherein the ball component has a volume removedsuch that it may be inserted through the opening into the socketcomponent.
 9. The assembly of claim 6, wherein the undercut in the ballcomponent forms a generally saddle shape.
 10. The assembly of claim 6,wherein one of the ball and socket components is formed fromnon-deformable material or both of the ball and socket components areformed from non-deformable material.
 11. The assembly of claim 6,wherein the socket component includes an internal bearing surfaceextending more than 180 degrees in one dimension and less than 180degrees in a dimension perpendicular to the one dimension.
 12. A jointfor use in a patient, comprising: a substantially spherical headcomponent having a shaft extending therefrom, the head component and theshaft formed as a one-piece component; and a substantially sphericalchamber with an opening to allow insertion of the head component,wherein the spherical head component has a cavity defined by a volumethat is removed from a non-load bearing portion of the head component ona half of the head component closest to the shaft to allow insertion ofthe head component through the opening, wherein the volume that isremoved extends about less than a full circumference of the sphericalhead component.
 13. An assembly comprising: two at least partialspherical bodies, a first at least partial spherical body having aninternal surface area having a discontinuity defining an opening, and asecond at least partial spherical body having a volume; wherein amaximum diameter of the second at least partial spherical body issmaller than a maximum diameter of the first at least partial sphericalbody and the maximum diameter of the second at least partial sphericalbody is larger than a dimension of the discontinuity; and wherein thesecond at least partially spherical body includes a spherical portionand a shaft portion configured as a single one-piece component andincluding an undercut extending from the shaft portion about less than afull circumference of the second at least partial spherical body, theundercut having a longitudinal length parallel to the shaft portion thatis less than an undercut circumferential width transverse to thelongitudinal length.